A Siphon is an Illyrian magical jewel gifted to warriors with large amounts of power to give them an advantage in battle. They filter raw power and allow the user to transform their power into something more subtle and varied, into different objects, typically shields, weapons, or armor. Siphons concentrate and focus an Illyrian's power. This object manipulates magic to be more precise. Siphons don't contain an infinite amount of power and can run out. To use a Siphon, the person's power must be compatible with it. For instance, Rhysand is unable to use a Siphon, as his power overloads a Siphon, causing it to shatter.
Siphons can be a range of colors, the most common being red or blue. The color of the magic will be the same as the color of the Siphon. Although most users wear one Siphon, Cassian and Azriel each wear seven.
Rhysand tells Feyre that "the power of stronger Illyrians tends toward 'incinerate now, ask questions later.' They have little magical gifts beyond that, the killing power." He continues by telling her to "imagine the difference between hurling a bucket of paint against the wall and using a brush. The Siphons allow for the magic to be nimble, precise on the battlefield, when its natural state lends itself toward something far messier and unrefined, and potentially dangerous when you're fighting in tight quarters."
- The objects are named Siphons because they are able to channel the power and even empty it if necessary, essentially siphoning power.
- When an Illyrian takes part in the Blood Rite, they are not permitted to use any magic, including a siphon.
- In the real world, a siphon can also refer to a wide variety of devices that involve the flow of liquids through tubes.